Asphalt hydrogenation process



Aug. 23, 1960 c. L. THORPE ETAL 2,950,242

ASPHALT HYDROGENATION PROCESS Filed Oct. 7, 1957 PROPERTIES OF TOTAL LIQUID PRODUCTS FROM ASPHALT HYDROGENATION 2 taco PSIG,O.5 v/v/un,3ooo scF ,7oo-75a TEMP. GRADIENT) M.N. I. WT. A (FEED 12.2)

GRAVITY, AP| (FEED 6 5) '6 5 I I00 I25 I50 HOURS ON ASPHALT FEED X'CONTINUOUS UNINTERRUPTED OPERATION A-PERiODIC DEPRESSURING T0 0 P516 O-PERIODIG DEPRESSURING TO 200 P516 ASPHALTIC HYDROGEN FEED srocx '8 22 E 16, 2o

54 nuc'nou 36 amused? l b-5O E) rucg a n nlon 28 FIG. I.

INVENTORS. 32 Charles L. Thorpe,

Raymond L. Heinrich 26 24 I EL Edward J. Hoffman,

::-;g James A. Anderson,Jr.,

BY PRODUCT necswsa IL'TORNEY.

Patented Aug. 23, 1960 ASPHALT HYDROGENAT ION PROCESS Charles L. Thorpe, Raymond L. Heinrich, Edward J. Halfman and James A. Anderson, In, Baytown, Tex assignors, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N.J., a corporation of Delaware Filed Oct. 7, 1957, Ser. No. 688,449

15 Claims. (Cl. 208-108) This invention relates to a process for the conversion of asphalt into lower boiling more valuable products. More particularly, this invention relates to a regenerative catalytic asphalt conversion process wherein catalyst activity is maintained over prolonged periods of time.

Asphaltic hydrocarbons have but a small value when utilized as components of hydrocarbon fuel products such as heating oil, bunker fuel, etc. Accordingly, there is a substantial incentive for converting asphaltic hydrocarbons to more valuable products. It is particularly desirable to convert asphalt into catalytic cracking feed stocks in that the catalytic cracking of such feed stocks provides high octane gasoline boiling range products. Thermal cracking and coking processes utilized in the conversion of asphaltic hydrocarbons are normally characterized by comparatively high yields of gaseous hydrocarbons, comparatively high yields of low octane quality naphthas and only low to moderate yields of gas oils suitable for cracking.

In accordance with the present invention there is provided an improved regenerative catalytic asphalt conversion process of the type characterized by high yields of gas oil boiling range material, compartively low yields of naphtha boiling range material and small yields of gaseous hydrocarbons, the present invention being particularly directed to an improved method of asphalt conversion wherein catalytic activity is sustained by a particular reaction-reactivation sequence, of operations for prolonged periods of time without the need, for oxygen regeneration of the catalyst.

When operating in a continuous manner for prolonged periods of time, an undesirably rapid accumulation of carbonaceous materials on the catalysts results in the need for undesirably frequent air regeneration of the catalyst.

This is avoided in accordance with the. present invention by conducting asphalt conversion operations under the described conditions for a period of from about 1 to about 20 hours, followed by rapid depressuring of the catalytic reaction zone to from about 50 to 5 percent of normal operating pressure within a depressuring time of from about 0.5 to 5 minutes followed by immediate repressuring of the catalytic reaction zone to normal operating pressure Within from about 1 to 40 minutes. Preferably, asphalt conversion operations are conducted in an operating sequence including the steps of converting the asphaltic feed stock at normal operating pressure for from about 5 to 15 hours, depressuring the catalytic reaction zone to from about 30 to 20 percent of normal operating pressure Within from about 1 to 5 minutes and then immediately repressuring the catalytic reaction zone to normal operating pressure within from about 2 to 15 minutes.

The asphaltic hydrocarbon feed stocks to be utilized in accordance with the present invention boil above about 1050 F. and may be characterized as concentrated asphalt fractions. Suitable asphaltic hydrocarbon feed stocks for the present invention include bitumen, asphaltic residua obtained by the vacuum distillation of petroleum hydrocarbon crude oils, asphalts obtained by solvent deasphalting of crude residuum fractions, tarry substances obtained in the oxidation of high molecular weight hydrocarbons, asphalts obtained from hydrogenated coal products, etc. and suitable mixtures of such materials.

Since the asphaltic material by itself is normally a semi-solid or solid material with relatively high viscosity and softening point at atmospheric temperatures, it is generally preferable to blend with the asphalt fraction an amount of diluent boiling below 1050 F. sufiicient to provide a pumpable mixture of diluent and asphalt. It is generally necessary to employ at least about 10 volume percent of diluent and as much as about 100 volume percent of diluent may be employed. Preferably, however, from about 15 to 25 volume percent of diluent is employed. The diluent may boil within the range of about 400 to 1050 F. and may comprise naphtha fractions, kerosene fractions, heating oil fractions, gas oil fractions, and suitable mixtures thereof.

The catalyst to be employed in the practice of the present invention should be a sulfactive hydrogenation catalyst of the type conventionally used for hydrodesulfurlzation, destructive hydrogenation, hydrocracking and related processes. Examples of such catalysts include cobalt molybdate, nickel tungsten sulfide, molybdenum sulfide, etc., which catalysts are preferably supported on a suitable carrier such as activated gamma alumina. (The term activated, as here used, denotes a gamma alumina having a microporous structure affording a large inner surface.) A cobalt molybdate catalyst is preferred. It will .be understood that such cobalt molybdate catalysts may actually comprise a mixture of the oxides of cobalt and molybdenum. The gamma alumina supported catalyst composition of the present invention should preferably contain from about 1 to 20 weight percent sulfactive hydrogenation catalyst.

The reaction conditions to be employed include, generally, a temperature within the range of about 600 to 850 F., a pressure Within the range of about 200 to 2000 p.s. i.g., a liquid space velocity within the range of 0.2 to 5 v./v./hr., and a hydrogen charge rate of about 1000 to 10,000 cubic feet of hydrogen per barrel of feed stock. A temperature gradient is preferably maintained in the reaction zone, the inlet temperature being from about 20 to F. (and preferably about 40 to 60 P.) less than the outlet temperature. The reaction conditions may be adjusted Within the above indicated limits to provide for varying degrees of conversion which, in turn, may be utilized to provide for difierent degrees of reaction selectivity. in general, the extent to which the asphaltic feed stock is converted will determine the nature and quality of the products that are obtained. Thus, for example, under comparatively mild operating conditions wherein about a 5 to 20 volume percent conversion of the asphaltic feed stock is obtained, the principal conversion product is a gas oil boiling range product which is suitable for use as a catalytic cracking feed stock. Only minor amounts of high boiling products are obtained and normally less than about 2 percent of the products are gaseous hydrocarbons. Still further, a significant reduction in the sulfur content and the naphtha insolubles content (as hereinafter defined) is obtained with respect to the asphaltic product material boiling above 1050 F. whereby such asphaltic product is materially improved in physical properties to an extent sufficient to permit its more economical use as a fuel oil component.

Under intermediate conversion conditions wherein about 20 to 50 volume percent of the feed stock is converted to'lower boiling products, the products are char; acterized by high yields of gas oil boiling, range distillates and comparatively small yields of naphtha. In this situation the sulfur content and the naphtha insolubles content of the asphaltic product will generally be equivalent to those of the asphaltic feed stock. Under severe operating conditions wherein more than about 50 volume percent conversion is obtained, the distillate product is still primarily a gas oil boiling range distillate fraction; however, substantial yields of naphtha are obtained. Even in this case, however, the conversion to gaseous hydrocarbons is normally less than about percent. The asphaltic product resulting from severe conversion will normally be inferior to the asphaltic feed stock with respect to physical properties. seen, therefore, that the asphalt conversion process of {the present invention is afiexible process which may be conducted so as to obtain the most efiicient and economical use of the asphalt feed material.

From the foregoing it is a temperature of about 700 to 750 F. The outlet temperature is preferably about 40 to 60 F. greater than the inlet temperature. The heated mixture is discharged from the heating zone 14 by way of a line 22 leading to the reaction zone 10. As indicated, the amount of hydrogen charged by way of the line 18 may suitably be within the range of 2000 to 4000 cubic feet of hydrogen per barrel of feed stock and is employed in an amount suflicient to provide for the desired reaction pressure within the reaction zone 10 which is preferably in the range from about 600 to about 950 p.s.i.g. (e.g., 800 p.s.i.g.). The liquid space velocity charge rate of the asphaltic feed stock to the reaction zone 10 may suitably be from about 0.5 to 2 v./v./hr.

In flowing through the reaction zone 10, at least a portion of the asphaltic feed stock is converted to lower boiling more valuable products. In addition, desulfuriza Although temperature, pressure, space velocity and hydrogen charge rate will all have an efiect upon conversion, the reaction conditions most easily regulated in controlling conversion are space velocity and temperature. In general, a decrease in space velocity will increase the severity of conversion conditions and an increase in temperature will increase the severity of conversion conditions. Thus, for example, at a pressure. within the range of about 400 to 800 p.s.i.g. and with a hydrogen charge rate within therange of about 2000 to 4000 cubic feet of hydrogen per barrel of feed stock, a conversion of from about 5 to 20 percent of the asphaltic feed stock maybe obtained by employing an inlet temperature of from about, 650 to about 700 R, an outlet temperature of about 675 to 725 F., and a liquid space velocity within the range of about 1.0 to 2.0 with a feed stock F., and the space velocity within the range of about 0.5

to 1.0 v./v./hr.' 7 V V The invention will be further describedin connection with the accompanying drawing wherein:

Fig. l is a schematic flow sheet illustrating one manner in which theprocess of the present invention may be conducted; and

Fig. 2 is a graph showing the eflect of various operating procedures on catalyst activity over prolonged periods of time.

Turning first to Fig. '1, there is schematically disclosed a reaction zone 10 containing a fixed bed of a suitable catalyst such as, for example, a particulate catalyst composition consisting of about 15 weight percent of cobalt molybdate supported on gamma alumina. A pumpable asphaltic feed stock containing, at least about 50 volume percent of material boilingabove 1050? F. and, preferably, from about 75 to 100 volumepercent of 1050 Fjmaterial is charged from a suitable source such as a "stock tank. 12 to a. heating zone 14 by way of a line 16.

Hydrogen is admitted to the system by way of a line 18 controlled by a valve 20. Within the heating zone 14 the mixture of asphaltic feed 'stock and hydrogen is brought to' a suitable inlet reaction temperature, such as 4 feed stock through the reaction zone 10.

tion and the conversion of'naphthainsoluble materials also occurs. I V, H 7 7 The reaction productsare discharged from reaction zone 10 by way of a line 24 leading to a product receiver 26 of any suitable. construction wherein hydrogen and gaseous conversion products are separated from the liquid products. The gaseous products are discharged from the product receiver 26 by way of a line 28 controlled by a valve 30, the rate of discharge of gaseous products through the line 28 being such that the desired pressure is maintained within the reaction zone 10. Liquid conversion products are discharged from the product receiver 26 by way of a line 32 leading to a fractionation zone 34 of any suitable construction. The fractionation zone 34 is shown in the drawing as a single distillation column. ltvwill be understood that in actual practice it will frequently be desirable to employ a plurality of sequentially interconnected fractionating columns, the single column having been shown in Fig 1 in order to simplify the a drawing. Within the fractionation zone 34 the liquid products are separated in any desired manner so as to provide, for example, a naphtha boiling range product fraction boiling above about430 F. which is discharged by way of a line 36, a heating oil fraction boiling within the range of about 430 to 650 F. discharged by way 10f a line 38, a light gas oil fraction boiling within the range of about 650 to 950 F. discharged byway of a line 40, and a heavy gasoil fraction boiling Within the range of about 950 to 1015 F. discharged byway of a line 42. A residuum fraction boiling above about l015 F. may be discharged from the'fractionationzone :34 by way of a bottoms line 44 controlled by a valve 46 and may be discharged from the system by opening the valve 46 or may be recycled by closing the valve 46 in order to route the residuum fraction to a recycle line 48 controlled by a valve 50 leading to the stock tank discharge line 16.

. In accordance with the present invention, asphalt conversion operations are conducted in the described manner for a period of time of about 1 to 20 hours (preferi ably from about 4 to 10 hours). At the end of this time the reaction zone 10 is rapidly depressured to about 50 to 5 percent of normal operating pressure (preferably 30 to 20 percent) within a period of time within the range of about 0.5 to 20 minutes while continuing the flow of Immediately thereafter, the reaction zone 10 is repressured to, normal operating pressure within 0.5 to 20 minutes (preferably 31 to 5 minutes). The depressuring step is preferably accomplished by maintaining a substantially constant hydrogen charge rate through the line 18 and by opening the valve 30 to thereby rapidly vent gaseous products from the product receiver 26 by way of the line 28. In this manner rapid and effective depressuring is obtained. The repressuring step is preferably conducted by adjusting the setting of the valve30 in the line 28 to its normal setting and by temporarily accelerating the hydrogen charge rate through .the line 18 by adjustment of the assau ts valve to again build up the desired pressure in the reaction zone 10.

In accordance with one form of the present invention, flow of the asphaltic feed stock through the catalytic reaction zone is continued through the rapid depressuringrepressuring step so that there is a continuous flow of asphaltic hydrocarbon feed stock through the reaction zone.

In accordance with another form of the present invention, the depressuring-repressu1ing step is conducted in the additional presence of a petroleum hydrocarbon wash liquid boiling Within the range of about 400 to 1000 F., and preferably within the range of about 650 to 1000 F. When a wash liquid is to be employed, the wash liquid is introduced into the catalytic reaction zone along with the asphaltic hydrocarbon feed stock from about 1 to 15 minutes prior to initiation of the depressuringrepressuring operation and flow of the wash liquid through the catalytic conversion zone is terminated from about 1 to 15 minutes after the termination of the repressuring operation.

When it is desired to blend an additional amount of diluent with the asphaltic feed stock during the rapid depressuring-repressuring step, from about 10 to 100 volume percent, based on the asphaltic feed stock, of diluent may be employed. The diluent is introduced into the system in this situation by way of a diluent charge line 5?. controlled by a valve 54 leading to the stock tank discharge line 16. The charging of additional diluent is initiated from about 1 to 15 minutes prior to the rapid depressuring-repressuring step and is discontinued from about 1 to 15 minutes after the termination of the depressuring-repressuring step. In conducting the process of the present invention in a continuous manner, therefore, the normal operating conditions will be interrupted every 1 to 20 hours to provide for the just described depressuzingrepressuring step. Asphalt conversion operations may be conducted in this fashion for prolonged periods of time such as, for example, up to about 500 to 5000 hours total hours of reaction time. It may then be desired to regenerate the catalyst within the reaction zone iil by burning carbonaceous deposits therefrom. This is accomplished, in general, by discontinuing the flow of asphaltic feed stock and hydrogen through the reaction zone in, by purging the reaction zone of such reactants and by then admitting an oxygen-containing gas to the reaction zone by any suitable means (not shown) at a temperature sufficiently high to permit the burning of substantially all of the carbon without damage to the catalyst. After oxygen regeneration of the catalyst in this fashion, the asphalt conversion operations may be resumed and conducted in the described manner.

The invention will be further illustrated by the following speciiic examples which are given by way of illustration and which are not intended as limitations on the scope of this invention.

In order to evaluate the catalyst activity maintenance reaction sequence of the present invention, a series of comparative runs were conducted utilizing a commercially available 30 to 20 mesh cobalt molybdate catalyst containing about weight percent of cobalt molybdate supported on gamma alumina.

In the first series of comparative runs, the reaction conditions selected included a reactor inlet temperature of about 760 3, a reactor outlet tern erature of about 750 F., a pressure of about 800 p.s.i.g., a liquid space velocity of about 8.5 v.v./hr. and a hydrogen charge rate of about 3960 cubic feet or" hydrogen per barrel of feed stock.

In order to provide a basis for comparison, a standardized feed stock was first charged to the catalyst under the described reaction conditions on a continuous basis Without interruption for a period of about 110 hours. In a second run, and in order to provide a further basis for comparison, the standardized feed stocl: was charged under the described reaction conditions. However, in this instance at the end of each 2 hours of reaction time, the pressure within the reaction zone was reduced to atmospheric pressure within 0.5 to 1 minute and the reaction zone was repressured within about 2 to 3 minutes.

A run was then conducted in accordance with the present invention wherein, during the first 50 hours of operations, a depressuring-repressuring step was employed at 1 hours intervals, the step being accomplished by reducing reaction pressure from 800 to 209 p.s.i.g. within about 36 seconds to l minute, followed by immediate repressuring to 569 p.s.-i.g. within about 2 to 3 minutes. For the remaining period of the run, the de pressuring-repressuring step was conducted at 4 hour intervals.

During the course of the runs, the physical properties of the total liquid product were measured at periodic intervals. The results of this test are graphically represented in attached Fig. 2.

As shown by Fig. 2, a substantial improvement in catalyst activity maintenance was possible through the provision of the process of the present invention. it will be seen that the most efiicient reduction of naphtha insolubles, the most efficient reduct on of sulfur content and the most efiicient increase in total liquid product specific gravity was obtained in the case of the present invention wherein periodic depressuring to 209' p.s.i.g. was employed.

To further illustrate the improvements obtainable with the present invention, at the end of each of the abovedescribed runs, samples of the catalysts were removed from the reaction zone and washed repeatedly with a suitable solvent (toluene) in order to remove soluble carbonaceous deposits from the sample. The carbon remaining on the catalyst after the washing operation represents carbon which is removable as a practical matter only by oxygen regeneration. At the end of the washing operation, the catalyst was dried and the surface area and the carbon content thereof were measured. The results of this operation are set forth in Table I.

TABLE I Non-strippable carbon on spent catalyst after 146 hours Fresh 1 2 Catalyst Run Surface Area, mK/grn Carbon Content, Wt. Percent Metals Content, Wt. Percent:

Vanadium Nickel Iron From Table I it will be observed that in run No. 3, conducted in accordance with the present invention, the carbon content was only 6.7 weight percent whereas in the case of run No. 2 (involving depressuring to atmospheric pressure), carbon content was almost twice as much (13.9 weight percent) and that, in addition, the catalyst from run No. 1 had a lower surface area. Although the catalyst from run No. 1 had a lower carbon content than the catalyst of run No. 3, it is to be ob served that, as pointed out above, the extent of desulfurization, naphtha insoluhles conversion and product gravity increase was substantially less than was the case of run No. 3.

By way of illustration of the results obtainable, in following Table 11 there is set forth a detailed characterization of the standardized feed stock employed in conducting the tests and the yields and qualities of the liquid fractions obtained during each of the runs. While not reported in the table, it is to be observed that in all instances gaseous hydrocarbon yield was less than about 2 volume percent of the feed.

TABLE 11 Feed 1 2 Stock IBP430 F.:

Vol. Percent Gravity, API Sulfur, Wt. Percent Bromine No 430650 F.:

Vol. Percent Gravity, API

Sulfur, Wt. Percent Bromine No 650950 F;

V01. Percent Gravity, API..-

Sulfur, Wt. Percen Oonradson Carbon, Wt Percent- 950-1,015 F;

Vol. Percent Gravity, API

Sulfur, Wt. Percent Conradson Carbon. Wt. Percent 1,015 F.+:

Vol. Percent Specific Gravity Sulfur, lVt. Percent.

MN I, Vt. Percent 1 Conradson Carbon, Wt. Percent- 1 Modified naptha insolubles. 2 6501,015 F.

Having described our invention, what is claimed is:

1. In a continuous process for the conversion of a pumpable concentrated asphaltic feed stock to lower boiling more valuable products in a conversion zone at a pressure within the range of about 200 to 2000 p.s.i.g. in the presence of a fixed bed of a sulfactive hyrogenation catalyst under conversion conditions including a temerature within the range of about 600 to 850 F., the conversion zone outlet temperature being from about 20 to 80 F. greater than the conversion zone inlet temperature, a liquid space velocity charge rate within the range of about 0.2 to 5 v./v./hr. and a hydrogen charge rate Within the range of about 1000 to 10,000 cubic feet of hydrogen per barrel of feed stock, the improvement which comprises periodically depressun'ng said conversion zone during said continuous conversion of said asphaltic feed stock operations at intervals of from about 1 to 20 hours and then repressuring said conversion zone to normal operating pressure, sa=id conversion zone being depressured to about 50 to 5 percent normal operating pressure within about 0.5 to 5 minutes and'then being repressured to normal operating pressure within about 1 to 40 minutes.

2. A method as in claim 1 wherein said depressuringrepressuring steps are conducted while simultaneously charging a'hydrocarbon diluent boiling within the range of 450 to 1050 F. to said conversion zone. j V V 3. In a continuous process for the conversion of a pumpable concentrated asphaltic feed stock to lower boiling more valuable products in a conversion zone at a pressure within the range of about 600 to about 950 p.s.i.g. in the presence of a fixed bed of a sulfactive hydrogenation catalyst under conversion conditions including a temperature with in the range of about 700 to 750 F., the conversion zone outlet temperature being from about 40 to 60 F. greater than the conversion zone inlet temperature, a liquid space velocity charge rate within the range of about 0.5 to 2 v./v./hr. and a hydrogen charge rate within the range of about 2000 to 4000 cubic feet of hydrogen per barrel of feed stock, the improvement which comprises periodically depressuring said conversion Zone during said continuous conversion of said asphaltic feed stock operations at intervals of from about 1 to 20 hours and then repressuring said conversion zone to normal operating pressure, said conversion zone being de- 4. A method as in claim 3 wherein hydrocarbon diluent boiling within the range of 400 to 1050 F. is periodically introduced into said conversion zone about 1 to 15 minutes prior to the initiation of each of saiddepressuring steps, the addition of diluent being terminated within about 1 to 15 minutesafter the termination of each of said repressuring steps.

5. In a continuous process for the conversion of a pumpable concentrated asphaltic feed stock to lower boiling more. valuable products in a conversion zone at a pressure within the range of about 600 to about 950 p.s.i.g. in the presence of a fixed bed of a vsulfactive hydrogenation catalyst under conversion conditions including a temperature. within the range. of about 700 to 750 F., the

conversion 'zone 'outlet temperature being from about 40 to F. greater than the conversion zone inlet temperature, a liquid space velocity charge rate within the range of about 0.5 to 2 v./v./hr. and a hydrogen charge rate within the range of about 2000 to 4000 cubic feet of hydrogen per barrel of feed stock, the improvement which comprises periodically depressuring said conversion zone during said continuous conversion of said pressure within about 1 to 5 minutes and then being repressured to normal operating pressure within about 2 to 15 minutes.

6. A method as in claim 5 wherein said feed stock consists essentially of a mixture of a concentrated asphalt fraction boiling above about 1050 F. with an amount of a lower boiling hydrocarbon diluent suflicient to render said concentrated asphalt pumpable.

7. A method as in claim 6 wherein said diluent is employed in an amount within the range of about 10 to 100 volume percent, based on said concentrated asphalt fraction.

8. A method as in claim 6 wherein said concentrated asphalt fraction is diluted with from about 15 to 25 volume percent of a lower boiling hydrocarbon diluent boiling within the range from about 400 to 1050 F.

9. A method as in claim 8 wherein an additional 10 to 100 volume percent of a diluent boiling within the range of about 400 to 1050 F., based on said concentrated asphalt fraction, is introduced into said conversion zone from about 1 to 15 minutes prior to the initiation of each of said depressuring steps, introduction of said additional quantity of diluent being terminated from about 1 to 15 minutes after each of said repressuring steps. 7

10. In a continuous process for the conversion of a pumpable concentrated .asphaltic feed stock. to lower boiling more valuable products in a conversion zone at a pressure within the range of about 600 to 950 p.s.i.g. in the presence of a fixed bed of a gamma alumina supported cobalt molybdate catalyst under conversion conditions including a temperature within the range of about 700 to 750 F., the conversion zone outlet temperapressured to about 50 to 5 percent normal operating p-resconversion zone inlet temperature, a liquid space velocity charge rate within the range of about 0.5 to 2 v./v./hr.

and a hydrogen charge rate within the range of about 2000 to 4000 cubic feet of hydrogen per barrel of feed stock, the improvement which comprises periodically depressuring said conversion zone during said continu- 0115 of conversion of said asphaltic feed stock operations at intervals of from about 5 to 15 hours and then repressuring said conversion zone to normal operating pressure, said conversion zone being depressured to about 30 to 20 percent normal operating pressure within about 1 to 5 minutes and then being repressured to normal op erating pressure within about 2 to 15 minutes.

11. A method as in claim 10 wherein said feed stock consists essentially of .a mixture of a concentrated as- 9 phalt traction boiling above about 1050 F. with an amount of a lower boiling hydrocarbon diluent sufiicient to render said concentrated asphalt pumpable.

12. A method as in claim 11 wherein said diluent is employed in an amount within the range of about 10 to 100 volume percent, based on said concentrated asphalt fiaction.

13. A method as in claim 11 wherein said concentrated asphalt fraction is diluted with from about 15 to 25 volume percent of a lower boiling hydrocarbon diluent boiling within the range of about 400 to 1050 F.

14. A method as in claim 13 wherein an additional 10 to 100 volume percent of a diluent boiling Within the range of about 400 to 1050" F., based on said concentrated asphalt fraction, is introduced into said conversion zone from about 1 to 15 minutes prior to the initiation of each of said depressuring steps, introduction of said additional quantity of diluent being terminated from about 1 to 15 minutes after each of said repressuring steps.

15. In a continuous process for the conversion of a pnmpable concentrated asphaltic feed stock to lower boiling more valuable products in a conversion zone in the presence of a fixed bed of a sulfactive hydrogenation catalyst, said catalyst being contained in a reaction zone provided with a charge line for feed materials and, downstream from the catalyst bed, a vented product receiver for separating normally gaseous reaction products from normally liquid reaction products, the conversion conditions maintained in said reaction zone including a pressure within the range of about 200 and 2000 p.s.i.g., a temperature in the range of about 600 to 850 F., the outlet temperature being about 20 to 80 F. greater than the inlet temperature, a liquid space velocity charge rate within the rate of about 0.2 to 5 v./v./ hr. and a hydrogen charge rate within the range of about 1000 to 10,000 cubic feet of hydrogen per barrel of feed stock, the improved method for continuous conversion of said asphaltic feed stock which comprises, at one to 20 hour intervals, increasing the amount of material vented from said product receiver by an amount sufficient to reduce the pressure in said conversion zone to about 50 to 5 percent of normal operating pressure within a period of about 0.5 to 5 minutes, and immediately thereafter discontinuing said increased venting and simultaneously increasing the normal hydrogen charge rate by an amount sufficient to reestablish normal operating pressure within a period of about 1 to minutes and thereafter reestablishing normal hydrogen charge rate.

References Cited in the file of this patent UNITED STATES PATENTS 2,602,771 Munday et a1. July 8, 1952 2,768,936 Anderson et a1. Oct. 30, 1956 2,791,546 Anhorn May 7, 1957 2,882,221 Dinwiddie et al Apr. 14, 1959 

1. IN A CONTINUOUS PROCESS FOR THE CONVERSION OF A PUMPABLE CONCENTRATED ASPHALTIC FEED STOCK TO LOWER BOILING MORE VALUABLE PRODUCTS IN A CONVERSION ZONE AT A PRESSURE WITHIN THE RANGE OF ABOUT 200 TO 2000 P.S.I.G. IN THE PRESENCE OF A FIXED BED OF A SULFACTIVE HYROGENATION CATALYST UNDER CONVERSION CONDITIONS INCLUDING A TEMPERATURE WITHIN THE RANGE OF ABOUT 600* TO 850*., THE CONVERSION ZONE OUTLET TEMPERATURE BEING FROM ABOUT 20* TO 80*F. GREATER THAN THE CONVERSION ZONE INLET TEMPERATURE, A LIQUID SPACE VELOCITY CHARGE RATE WITHIN THE RANGE OF ABOUT 0.2 TO 5 V./V./HR. AND A HYDROGEN CHARGE RATE WITHIN THE RANGE OF ABOUT 1000 TO 10,000 CUBIC FEET OF HYDROGEN PER BARREL OF FEED STOCK, THE IMPROVEMENT WHICH COMPRISES PERIODICALLY DEPRESSURING SAID CONVERSION ZONE DURING SAID CONTINUOUS CONVERSION OF SAID ASPHALTIC FEED STOCK OPERATIONS AT INTERVALS OF FROM ABOUT 1 TO 20 HOURS AND THEN REPRESSURING SAID CONVERSION ZONE TO NORMAL OPERATING PRESSURE, SAID CONVERSION ZONE BEING DEPRESSURED TO ABOUT 50 TO 5 PERCENT NORMAL OPERATING PRESSURE WITHIN ABOUT 0.5 TO 5 MINUTES AND THEN BEING REPRESSURED TO NORMAL OPERATING PRESSURE WITHIN ABOUT 1 TO 40 MINUTES. 